Lecture 20 Flashcards
What is the significance of the equator that runs through the neurocrystalline lattice structure of the Drosophila eye
The equator is a line of mirror symmetry that runs through the centre of the eye where the R7 indents of each surrounding ommatidia is positioned so as to face it
Roughly how long is it between successive induction of the photoreceptors of the ommatidia
2 hours
How is the lens of the Drosophila eye formed
The cones cells of the ommatidia secrete the overlying lens
Within which cells of the ommatidia are the UV-sensitive pigments contained in
R7
Other than eyeless, list some of the other genes involved in specification of the eyes
Twin of eyeless, eyegone, sine oculis, optix and Dachshund
Which cells of the ommatidia are the first to form
R8
Describe the organisation of the rhabdomeres within the ommatidia
R1 – R6 cells are organised around the outside of the ommatidia whilst R7 and 8 are present in the centre. R8 is stacked on top of R7
In which cells of the ommatidia is sevenless expressed in
R8, R1, R6, R4, R3 and R7 as well as in cone cells
Wild type Drosophila are phototactic with a preference for UV light, what is seen in R7 mutants
They will go towards white (visible) light due to an inability to see UV light
Where do the axons of the outer photoreceptors (R1-R6) project to
The lamina
Describe the structure of the Drosophila eye
Drosophila eyes are referred to as ocelli or orientation eyes as they don’t image as such. Each eye consists of 800 ommatidia or simple eye subunits orientated at angles to eachother to increase the size of the visual field.
What is the name of the structure where the axons of the R7 and R8 neurons cross over
Optic chiasm
Which two cells are then recruited after the R8 cell has been specified
R2 and R5
R6 and R1 are then recruited before R7 is specified last, T or F
T
What is the name of the EGF receptor ligand secreted by R8, 2 and 5 that leads to subsequent recruitment of cells
Spitz
Neurons in the eye are mapped in the same spatial orientation as the photoreceptors in the brain, T or F
T
What type of protein is boss
Bride of sevenless is a membrane-tethered ligand specific for sev
In which cell(s) of the ommatidia is boss expressed in
R8
What is seen in mice with a homozygous mutation in the gene that specifies eye development
Small eyes
If boss gene function is lost in R8, what is observed
R7 will not develop
Explain how sev and boss interact to dictate R7 development
Boss binds to sev and initiates a signal transduction cascade in the future R7 cell that is homologous to the Ras/MAP Kinase pathway. Son of sevenless (sos) links the sevenless RTK to the Ras protein by binding via its SH3 domain
Flies with mutant R1, 2 and 3 wont develop R7 is R8 isnt present, T or F
T – having wild type R1, 2 and 3 is not sufficient to generate an R7
What is the morphogenetic furrow and what is its role in development of the Drosophila eye
The morphogenetic furrow is a line that starts in the posterior eye disc in the first/second instar and sweeps across anteriorly with newly formed photoreceptors forming behind it
What is the term given to a gene that is both sufficient and necessary to dictate the formation of particular structures
Master regulatory genes
How are the R8 photoreceptors specified to form
Notch-delta signalling between the cells within the morphogenetic furrow acts as a lateral inhibition mechanism to space future R8 cells
The inhibition caused by the R8 cell is not just lateral but moves as the morphogenetic furrow does, T or F
T
Which gene must be expressed by the R8 cell in order to generate R7
Bride of sevenless
Which paired box transcription factor gene determines eye development in vertebrates
Pax6
Notch-delta signalling is involved in specification of the R8 cell. Which Notch ligand is used
Serrate
Homozygous mutants for Pax6 die perinatally with no eyes having developed, T or F
T
Retinal neurons cross over in a structure called to optic decussation, T or F
F – they cross in the optic stalk
Bride of sevenless and sevenless are two genes identified to be involved in the ability to Drosophila to perceive light. What is seen in sev and boss mutant flies
They will move to be in white light over UV light as opposed to the other way around as is seen in wild type
Pax6 has been determined to be both necessary and sufficient to dictate eye development, what is the experimental evidence for this in Drosophila
Misexpression of human Pax6 in Drosophila leads to the development of ectopic eyes throughout the fly
What are the results of mutations in Pax6 in humans
Aniridia – loss of the iris
What is the role of the pigment cells in the ommatidia
The pigment cell lattice optically insulates each unit eye ensuring that only light entering each subunit is coming from directly in front of it
What can be said about the cell division seen ahead of, within and behind the morphogenetic furrow
Ahead of the morphogenetic furrow the cells are dividing, within the furrow the cells have arrested in G1 of the cell cycle. Behind the morphogenetic furrow there is limited cell division
What is the significance of using notch-delta signalling in lateral inhibition
Notch delta signalling uses transmembrane ligands which limits the distance over which it can act to a single cell diameter
Explain the mechanisms present that act to specify R7
The boss signal restricted to apical membrane of R8 cell so that not all sev-expressing cells are exposed to boss. Seven-up (and rough) transcription factors are produced in the other photoreceptors and inhibit sevenless signalling
Sev and boss genes can be removed from R1-6 without causing loss of R7 specification, T or F
T
Where do the axons of the inner photoreceptors (R7 and R8) project to
The medulla
What type of protein is sevenless
RTK
What causes the appearance of the morphogenetic furrow
The morphogenetic furrow is caused by a shortening of the columnar epithelial cells
What is the name of the invertebrate homologue of the gene that determines eye development
Eyeless
Vision is extremely important to flies. What percentage of the fly brain is dedicated to visual processing
¾
Sev is absolutely required in R8, T or F
F – sevenless is absolutely required in R7, bride of sevenless is absolutely required in R8
Describe the organisation of each subunit of the Drosophila eye
Each ommatidia contains around 20 different cells, 8 photoreceptors, 2 primary, 6 secondary and 3 tertiary pigment cells. The photoreceptors are arranged into light sensitive structures known as rhabdomeres. Each ommatidia also has a bristle, neuron socket and sheath cell
Pax6 is a highly conserved homeobox containing transcription factor, T or F
T
Differentiation of the columnar epitehial cells into photoreceptors is seen in front of and within the morphogenetic furrow, T or F
F - Within and behind the furrow the first signs of differentiation are seen
